#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>

void find_single_dog(int arr[], int sz,int* single_dog)
{
	for (int i = 0; i < sz; i++)
		*single_dog ^= arr[i];
}


int main()
{
	int single_dog = 0;
	int arr[9] = { 1,2,3,4,5,1,2,3,4 };
	int sz = sizeof(arr) / sizeof(arr[0]);
	find_single_dog(arr, sz, &single_dog);
	printf("%d", single_dog);
	return 0;
}